User Manual
UMN:CLI
V5824G
159
Single Rate Three Color Marker (srTCM)
The srTCM meters an IP packet stream and marks its packet the one among green,
yellow, and red using Committed Information Rate (CIR) and two associated burst sizes,
Committed Burst Size (CBS) and Excess Burst Size (EBS). A packet is marked green if it
does not exceed the CBS, yellow if it exceeds the CBS, but not the EBS, and red
otherwise. The srTCM is useful for ingress policing of a service, where only the length,
not the peak rate, of the burst determines service eligibility.
CIR is the regenerating rate of tokens measured in bytes of IP packets per second. CBS
and EBS are the maximum size for each token bucket, C and E, measured in bytes. Both
token buckets share the common rate CIR. At least one of them (CBS and EBS) must be
configured, and it is recommended that the value is larger than or equal to the size of the
largest possible IP packet in the stream.
The token buckets C and E are initially full. When a packet arrives, the tokens in the
bucket C are decremented by the size of that packet with the green color-marking. If no
more tokens to transmit a packet remain in the bucket C, then the tokens in the bucket E
are decremented by the size of that packet with the yellow color-marking. If both buckets
are empty, a packet is marked red.
The following figures show the behavior of the srTCM.
Token
Packet
Token
CBS
EBS
Bucket C
Bucket E
Green Color-Marking
Tokens are regenerated
based on CIR
Tokens are regenerated
based on CIR
Tokens are decremented
by the size of the packet
Token
Fig. 7.4
Behavior of srTCM (1)
